Hydrolysis stable compositions for films in solar cells

Abstract

The present invention relates to polyester and carbodiimide containing transparent films for solar cells, which are characterized by improved resistance to hydrolysis, and also to the solar cells comprising these films. The carbodiimides have a number-average molar mass Mn of >1000 to <2000 g/mol, determined by GPC, measured in tetrahydrofuran (THF) against polystyrene as standard.

What is claimed is: 
     
         1 . A film comprising at least one polyester and at least one polymeric carbodiimide according to formula (I) 
       
         
           
           
               
               
           
         
         where:
 R 1  may be identical or different and is selected from the group comprising NHCONHR 3 , —NHCONR 3 R 4  or —NHCOOR 5 , wherein:
 R 3  and R 4  are identical or different and represent a C 1 -C 12 -alkyl, C 6 -C 12 -cycloalkyl, C 7 -C 18 -aralkyl radical or aryl radical, and 
 R 5  represents a C 1 -C 22 -alkyl, C 6 -C 12 -cycloalkyl, C 6 -C 18 -aryl or C 7 -C 18 -aralkyl radical, an unsaturated alkyl radical having 2-22 carbon atoms, or an alkoxypolyoxy- C 1 -C 12 -alkylene radical, 
 
 R 6 , R 7  and R 8  are each independently methyl or ethyl, but only a maximum of one of the radicals R 6 , R 7  and R 8  is methyl, and 
 n denotes 1 to 5, and 
 
         the carbodiimides have a number-average molar mass M n  of >1000 to <2000 g/mol, determined by GPC, measured in tetrahydrofuran (THF) against polystyrene as standard wherein the film is transparent and stable to hydrolysis. 
       
     
     
         2 . The film according to  claim 1 , wherein the polyester is selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polycyclohexanedimethanol terephthalate (PCT), ester-based thermoplastic elastomers, and biobased and/or biodegradable or compostable polyesters, and mixtures thereof. 
     
     
         3 . The film according to  claim 1 , wherein the film is biaxially oriented. 
     
     
         4 . The film according to  claim 1 , wherein the film comprises 0.5-2.5% by weight of the at least one polymeric carbodiimide of the formula (I), based on the polyester. 
     
     
         5 . The film according to  claim 1 , wherein the film comprises 1.0-2.0% by weight of the at least one polymeric carbodiimide of the formula (I), based on the polyester. 
     
     
         6 . The film according to  claim 1 , wherein:
 n=3;   R 1 ═—NHCOOR 5  where R 5 =cyclohexyl, and   R 6 , R 7  and R 8  are methyl or ethyl, with the proviso that a maximum of only one of the radicals R 6 , R 7  and R 8  is methyl.   
     
     
         7 . The film according to  claim 6 , wherein the polyester is selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polycyclohexanedimethanol terephthalate (PCT), thermoplastic urethane elastomers (TPE U), thermoplastic copolyester elastomer (TPE E), polybutylene adipate therephthalate PBAT, polylactides (PLA), and polyhydroxyalkoxides (PHA), and mixtures thereof. 
     
     
         8 . The film according to  claim 6 , wherein the at least one polyester comprises a mixture of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) or a mixture of polyethylene terephthalate (PET) and polylactide (PLA). 
     
     
         9 . The film according to  claim 8 , comprising 1-2% by weight, based on the polyester, of the carbodiimide. 
     
     
         10 . A solar cell module comprising the film according to  claim 1 . 
     
     
         11 . The solar cell module according to  claim 10  having a backing film comprising the film according to  claim 1 . 
     
     
         12 . A method for isolating solar cells from ambient environment, the method comprising enclosing at least a portion of the solar cells within the film according to  claim 1  for sealing of the solar cell. 
     
     
         13 . A transparent film comprising
 polylactide (PLA), polyethylene terephthalate (PET), or a combination thereof; and   about 0.05 to about 2.5% by weight of at least one polymeric carbodiimide according to formula (I)   
       
         
           
           
               
               
           
         
         where:
 R 1  may be identical or different and is selected from the group comprising NHCONHR 3 , —NHCONR 3 R 4  or —NHCOOR 5 , wherein:
 R 3  and R 4  are identical or different and represent a C 1 -C 12 -alkyl, C 6 -C 12 -cycloalkyl, C 7 -C 18 -aralkyl radical or aryl radical, and 
 R 5  represents a C 1 -C 22 -alkyl, C 6 -C 12 -cycloalkyl, C 6 -C 18 -aryl or C 7 -C 18 -aralkyl radical, an unsaturated alkyl radical having 2-22 carbon atoms, or an alkoxypolyoxy- C 1 -C 12 -alkylene radical, 
 
 R 6 , R 7  and R 8  are each independently methyl or ethyl, but only a maximum of one of the radicals R 6 , R 7  and R 8  is methyl, and 
 n denotes 1 to 5, and 
 
         the carbodiimides have a number-average molar mass M n  of >1000 to <2000 g/mol, determined by GPC, measured in tetrahydrofuran (THF) against polystyrene as standard 
       
       wherein the film is stable to hydrolysis. 
     
     
         13 . The film according to  claim 12 , comprising 1-2% by weight, based on the polylactide (PLA), polyethylene terephthalate (PET), or a combination thereof, of the carbodiimide. 
     
     
         14 . A solar cell module comprising the film according to  claim 12 .